Wood laths are put up in bundles of 100 laths; and are nailed upon the studdings of the wooden frame, with a space of one-quarter inch between them. This distance is sufficient to allow for lath shrinkage or swelling, and still provide a firm clinch for the plastering. If the space is much less than this, the plaster clinch will be weakened. If much more, the laths may possibly sag down on the ceilings with the extra weight of plaster. In no instance should these spaces between laths exceed a width of three-eighths of an inch.

The clinch, or key, of the plaster is formed by the mortar being pressed through the spaces between the laths and then spreading out back of the laths upon both sides of the crack, so forming a tie, or clinch, that holds the mortar firmly and securely in place.

It occasionally becomes necessary to lath on very thin furrings to cover over a heating pipe, a brick or iron support, or some other such exceptional instance of construction. In that case a wider space between the laths may strengthen the plaster clinch; or, better still, a strip of expanded metal may be used over or around such obstructions.



N. Le Brun & Sons, Architects, New York.

Walls of Stucco on Herringbone Expanded Steel Lath. For Plans, See Opposite Page.



S. Le Brun & Sons, Architects, New York.

The best wooden laths are made of pine or spruce, and are only partially seasoned. They should be free from sap, bark, and dead knots. Both bark and knots are likely to loosen from the surrounding wood and so destroy the hold of the plaster, while the face of the plaster is occasionally stained from pitchy knotholes, bark or sap.

All laths are now machine-sawn. The old-fashioned split lath has not been in the market for now more than fifty years.

If the laths are too dry, the wet mortar is likely to cause them to warp and twist; and if it hardens or sets before the laths become saturated, their swelling is likely to produce parallel plaster cracks. Better results can be obtained by using wet laths, when both mortar and laths dry out together.

In specifying the nailing of wood laths, it is sometimes thought to ensure better work if two nailings are required at each end of the lath, either upon the ceiling alone or upon both wall and ceiling. It is more than doubtful if this requirement produces the desired result, as two nails in the lath end are likely to start a split, which may be increased by the pressure necessary in applying the mortar, until the entire end of the lath is partially or wholly loosened from its support before the plastering is all upon the wall. Large lath nails, instead of making the work more secure, weaken it in the same way. The common-sized inch-and-one-eighth long "three-penny fine" - nails fasten the lath securely, even the ceiling nails rarely pulling out. About five pounds of nails will be necessary to each one thousand laths.

The joints of laths are ordinarily broken every eight courses.

This means that not more than eight adjoining lath ends are nailed upon one stud or furring, the next eight laths, in both directions, being carried by, ending upon the next wall stud or ceiling furring to either right or left, thus alternating the break and obviating the possibility of an extended crack occurring at the line of lath jointure. Some lathers find a small handful of these laths more convenient to handle than a larger bundle, in which case it is simpler and easier for them to break joints every six laths - which is equally good construction.

Occasionally studding is placed twelve inches apart, and the lath joints broken for every other lath. Such precautions, however, are not necessary in the ordinary dwelling. They increase expense; and the closer spacing of the studs, especially, provides more undesirable weight to be carried by the house frame.

Wherever the wood studding of partitions comes up against the brickwork of chimneys or a terra-cotta or brick wall, strips of expanded metal or wire-mesh lath should be employed, extending seven or eight inches over upon either side of such a joint; and, if such a joint occurs in an internal angle, future cracking from a difference in settlement or shrinkage may be prevented by cutting through each plaster coat, when soft, with a sharp trowel.